Question

why duck's quack doesn't echoes ?

Answer 1

despite in the myth to the contrary, scientist have demonstrated the drugs quacks produces echo

Answer 2

"A duck's quack doesn't echo" is a much-quoted scientific myth. The truth is that a duck's quack does, in fact, echo; however, it may be difficult to hear.

Like already said, any sound can echo. But duck's quacks are very quite and fading sounds which produces echos of very low intenity those are difficult to hear.